Are two cancer immunotherapy drugs better than one?

A class of immunotherapy drugs called checkpoint inhibitors has shown great promise against cancer in some patients. However, researchers' attempts to boost the drugs' efficacy by combining them with other immunotherapies have been disappointing. An article in Chemical & Engineering News (C&EN), the weekly news magazine of the American Chemical Society, describes the many challenges involved with harnessing the immune system to fight cancer.

In 2014, the U.S. Food and Drug Administration (FDA) approved two different PD-1 inhibitors, a type of checkpoint inhibitor that works remarkably well at shrinking certain types of tumors. Researchers wondered if those drugs—Merck & Co.'s Keytruda and Bristol-Myers Squibb's Opdivo—might work for more people with cancer if combined with another type of immunotherapy called IDO1 inhibitors. A slew of trials was launched to test the theory. But after the failure of a large study pairing Keytruda with Incyte's IDO1 inhibitor epacadostat, some are questioning the rush into studies combining immunotherapies, writes Senior Correspondent Lisa M. Jarvis.

Competition among drug companies has accelerated some immunotherapies through basic research and early-stage clinical trials before scientists fully understand how they work. As a result, combined immunotherapies that hint at benefits in animal models and early-phase clinical trials often don't pan out in Phase III trials—the large, expensive studies that are the final step before FDA approval. To increase the chances of bringing a successful combined immunotherapy to market, some experts say that well-planned, randomized mid-stage trials should be conducted before jumping the gun to large Phase III trials.